Arevalo Tungsten Geochem 2008

8/12/2019 Arevalo Tungsten Geochem 2008

1/10


2/10

ratios. Here we report high-precision concentration data for Ba, Th, U,

and W in an extensive suite of oceanic basalts in order to dene the

abundance of W in the modern mantle, bulk silicate Earth and core.

2. The abundance of W in the silicate Earth

2.1. The geochemical behavior of W

As a refractory element, the initial abundance of W in the bulkEarth can be calculated from chondritic relative abundances without a

volatility correction. Estimates of W in thesilicateportion of the Earth,

however, are poorly constrained. Difculties in determining the

abundance of W in the silicate Earth stem from the binary behavior

of the element; whereas W acts as a moderately siderophile element

under reducing conditions (i.e., during core formation), it has behaved

as an extremely incompatible lithophile element during the differ-

entiation of the silicate Earth (Palme and Rammensee, 1981).

Consequently, W is strongly enriched in the core and continental

crust, respectively, leaving the modern mantle depleted.

In the silicate Earth, the abundances of siderophile elements that are

compatible during mantle melting (Dsilcrystal/silliqN1; e.g., Niand Co) are

established from studies of massif peridotites and mantle xenoliths

because these elements are largely retained in olivine during partial

melting. However, in order to determinethe silicateEarth abundancesof

siderophile elements that behave incompatibly during mantle melting,

it is necessary to determine the abundances of these elements in both

the modern mantle and continental crust. Knowledge of the composi-

tion and relative mass contributions of themantleand crustal reservoirs

allows a reconstruction of the concentration of these elements in the

silicate Earth to be calculated (Newsom, 1990; Sims et al., 1990).

2.2. Incompatible element concentration ratios

The concentration of incompatible elements in basaltic melts is

controlled by the concentration of these elements in the source

mantle as well as a variety of fractionation processes, including partial

melting, fractional crystallization and crustal contamination. Concen-

tration ratios of similarly incompatible trace elements provide a reli-able estimate of the trace element composition of the source and can

complement information derived from radiogenic isotopes (Hofmann,

2003and references therein). Concentration ratios must be used with

care, however, because unlike isotope ratios they may be fractionated

during processes of magma genesis. A concentration ratio that is

uniform in all types of oceanic basalts (e.g., mid-ocean ridge basalts,

MORB, oceanic island basalts, OIB, and back-arc basin basalts, BABB)

and is independent of the absolute concentrations of the elements

involved represents a mantle value that has been unfractionated by

silicate differentiation. Such constant ratios (e.g., Zr/Hf, Sm/Hf, Rb/Ba,

Nb/Ta, etc.) reect element pairs with nearly identical bulk partition

coefcients during the genesis of basaltic partial melts and may be

inferred to be representative of their source ratios (Hofmann et al.,

1986; Newsom et al., 1986; Sun and McDonough, 1989). Constantconcentration ratios of highly incompatible elements are particularly

likely to represent the trace element ratios of their source regions, as

these elements are quantitatively removed from their source after

only a few percent of partial melting (Salters and Stracke 2004).

Because W is one of the most incompatible elements during

mantle melting, a concentration ratio involving W and another simi-

larly incompatible element (e.g., W/Ba, W/Th or W/U) likely charac-

terizes the ratio of the modern mantle if the ratio remains constant

throughout a range of MORB, OIB and BABB samples. Although no

other element behaves exactly like W in all geologic processes, pre-

vious work suggests that the geochemical behavior of W in silicate

systems is most comparable to that of Ba, Th and U ( Newsom and

Palme, 1984; Newsom et al., 1986, Sims et al., 1990; Newsom et al.,

1996; Noll et al., 1996).

2.3. Tungsten in the bulk continental crust

Newsom et al. (1996)estimated the abundance of W in the silicate

Earth by measuring relatively constant W/Th ratios in representative

samples of both the continental crust and modern mantle. In order to

characterize the abundance of W in the bulk crust, they examined

a comprehensive collection of samples representative of the lower,

middle and upper crustal reservoirs; over 145 crustal samples were

analyzed, including 18 lower crustal xenoliths, 20 rocks from high-grade metamorphic terrains, 45 samples of continental sediments, 13

rocks from oceanic volcanic arcs, 35 rocks from continental volcanic

arcs, 8 continental basalts, and 7 komatiites. Their study, which esta-

blished the concentration of W in the continental crust as ~1000 ng/g,

still serves as the standard for examining the abundance of W in the

bulk continental crust (Rudnick and Gao, 2003).

2.4. Tungsten in the modern mantle

Newsom et al. (1996)also estimated the abundance of W in the

modern mantle, but they analyzed only a limited sample set of

mantle-derived oceanic basalts (n =20) and altered mantle nodules

(n =7) with measured reproducibilities between 10 and 30% (2). As

opposed to mantle xenoliths, examining a broad spectrum of MORB,

OIB and BABB is instrumental to constraining the abundance of W in

different mantle reservoirs because oceanic basalts represent the most

signicant volume of terrestrial magmatism (an average rate of

~30 km3/yr of basalt has been produced over the past 180 Myr;Crisp,

1984) and carry the smallest risk of being contaminated during

magma transport (Jochum et al., 1989; Hofmann, 1997). In this study,

86 mantle-derived samples are analyzed, including 52 MORB, 16

intraplate basalts and 18 convergent margin samples. The reprodu-

cibility of our measurements (typically 5%, 2) are improved over

previous studies, and the extensive compilation of mantle-derived

materials considered here characterizes source regions from various

depths of the mantle, a wide spatial distribution across the globe and

every major tectonic setting.

3. Materials and methods

3.1. Sample descriptions

The mantle rocks analyzed in this study include both normal-type

MORB (N-MORB, K/Ti0.140) and enriched-type MORB (E-MORB, K/

TiN0.140), as well as a multitude of intraplate basalts, island arc

volcanics, and back-arc basin basalts. Most of the rocks are oceanic

basaltic glasses or ne-grained scoria, ranging from 40 to 59 wt.% SiO2and 3 to 10 wt.% MgO; thus, a range of magma compositions, from

primitive to differentiated, are represented by this sample set. More

information regarding the diversity of these samples, including a map

showing their global distribution, is provided in the accompanying

Supplementary materials.

3.2. Analytical method

Compared to rocks with coarser textures, glassy and/or ne-

grained samples provide comparatively homogeneous surface com-

positions that can be analyzed via laser ablation mass spectrometry.

This in-situ method of measuring trace element concentrations pro-

duces high-precision data and has been validated through numerous

analytical studies (e.g.,Pearce et al., 1997; Eggins et al., 1998; Norman

et al., 1998; Egginsand Shelley,2002; Jochumet al., 2005, 2006, 2007).

Laser ablation mass spectrometry also allows for: i) analyses of fresh,

unaltered materials, ii) low blanks, iii) millimeter-scale sample spe-

cimens, iv) spatially resolved, ng/g-level chemical measurements, and

v) surface and grain-boundary contamination to be avoided. All

samples examined in this study were analyzed using a New Wave

657R. Arevalo Jr., W.F. McDonough / Earth and Planetary Science Letters 272 (2008) 656665


3/10

frequency-quintupled NdYAG laser (213 nm light) coupled to a Ther-

mo Finnigan Element2 single-collector ICP-MS at the University of

Maryland.

The laser and mass spectrometer parameters utilized for the mea-

surements of this study are provided in Table 1. Prior to sample analysis,

themass spectrometerwas tuned to maximize signal(based on 43Caand232Th spectra) and minimize oxide production (232Th16O / 232Thb0.20%).

The detection parameters included a dwell time of 10 ms for 135, 137Ba,

30 ms for 232Th and 238U, and 100 ms for 182, 183, 184, 186W in order to

accumulate adequate counting statistics to evaluate and constrain

isobaric interferences, thus increasing analytical precision.

Spectralmatrix effects (i.e., isobaric interferences) were considered

and monitored during analysis in order to prevent a compromise in

accuracy. In this study, the only potential elemental isobaric inter-

ference is 186Os at mass 186W, but the concentration of Os in ourbasaltic melts was lower than our lower limit of detection. A poten-

tially more problematic source of isobaric interferences is diatomic

oxides. However, our analytical protocol measured the concentration

of W by monitoring four isotope mass stations: 182W,183W, 184W, and186W. Any potential oxide interferences on these masses would yield

discordant results between isotope ratios, but no systematic variances

were detected (see Supplementary materials). Further, we conducted

an experiment in which we analyzed a synthetic basaltic glass doped

with 500 ppmof theheavy rare-earth elements (HREE). Employingthe

analytical parameters described above, HREE-oxide production rates

(i.e., YbO/Yb and TmO/Tm) were measured to be ~106. Accordingly,

HREE-oxides do not present signicant isobaric interferences to even

the most depleted W concentrations in our natural samples.

Non-spectral matrix effects in concentration measurementsacquired through laser ablation ICP-MS can result from differences

in chemical compositions between the analyte and the standard

reference material. Although NIST SRM 612 (the standard reference

material utilized for our measurements) has been well characterized

and found to be homogeneous with respect to Ba, Th, U, and W, this

glass represents a more enriched composition (with approximately

40 g/g of each of these elements) than oceanic basalts, which can be

far more depleted, particularly in regard to Th, U and W. In order to

account for this discrepancy, which could potentially lead to analytical

biases, we have externally calibrated our W, Th and U measurements

to a suite of rocks analyzed via solution ICP-MS, includingboth isotope

dilution and high-precision standard addition analyses. More details

on the calibration of our trace element analyses are provided in the

Supplementary materials.

4. Results

4.1. Data precision and accuracy

Concentrations and uncertainties of Ba, Th, U, and W for all 86

samples investigated in this study are reported inTable 2. Concentra-

tions of W range from b10 ng/g in the most depleted MORB to

N2000 ng/g in the most enriched intraplate basalt. Most sample

concentrations were determined with

5% uncertainty (2

m; externalreproducibility of 816 measurements for W, and 24 measurements

for Ba, Th and U), though several analyses of phaneritic MORB glasses

with low W concentrations resulted in uncertainties greater than 10%.

The accuracy of our laser ablation method is demonstrated in Fig. 1,

where our Ba, Th, U, and W measurements are compared with

previously determined values from solution analyses, largely isotope

dilution measurements.

4.2. The best geochemical analogue to W

Correlations between Ba, Th, U, and W concentrations in basaltic

melts indicate that all four of these elements behave similarly during

the evolution of basaltic magma. In order to establish which

incompatible lithophile element most closely follows W in basaltic

sources, and thus which W/X ratio best represents a constant con-

centration ratio representative of the modern mantle, we can examine

the constancy of each W/X ratio across a wide range in W concen-

trations (Fig. 2).Sims and DePaolo (1997), however, noted that these

types of diagrams have the distinct disadvantages that (a) the plotted

variables are not statistically independent, and (b) variations in the y-

variable of each curve (i.e.,W/X, spanning ~1 order of magnitude) are

disproportionately small in comparison to variations in the x-variable

(i.e., W concentration, spanningN2 orders of magnitude). Additionally,

the slope of each linear regression inFig. 2is sensitive to the relative

value of the mean W/X ratio, resulting in articially high statistical

deviations from a slope of 0 for W/Th and W/U. Nevertheless, this plot

serves the qualitative purpose of illustrating that W/Ba, W/Th and W/

U all remain relatively constant over a range of concentrations. In

contrast, a ratio showing a systematic enrichment with increasing Wconcentration would indicate a lithophile element signicantly less

incompatible than W during mantle melting, and a systematic de-

pletion would designate a more incompatible lithophile element.

A more quantitative way to evaluate which lithophile element

behaves most analogously to W during silicate differentiation is

through a loglog co-variationplot (Simsand DePaolo,1997; Hofmann,

2003).Fig. 3illustrates such a diagram, with the concentrations of Ba,

Th and U plotted against the concentration of W in our basaltic sam-

ples. Using this diagnostic approach, a constant concentration ratio

will yield a slope of unity (m=1.00). According to our sample data, the

linear regression that is statistically closest to unity is that between W

and U. Both Th and Ba yield slopes greater than unity when plotted

against W, implying a higher incompatibility of these elements in

basaltic melts. Additionally, the W/U ratio of the mantle does notappear to be affectedby anydifferentiationprocesses, as the W/Uratios

of our samples are independent of MgO content as well as tectonic

setting (Fig. 4). Accordingly, we conclude that U is the incompatible

lithophile element that behaves most similarly to W through silicate

processing, despite the difference in mobility between these two

elements in aqueous phases (Taylor and McLennan, 1985).

5. Discussion

5.1. W in the silicate Earth, modern mantle, and core

Since U best mimics the geochemical behavior of W in our spec-

trum of basaltic samples, the average W/U ratio of our dataset like-

ly has not been affected by silicate differentiation events, and thus

Table 1

LA-ICP-MS specications

Laser ablation parameters

Ablation pattern Line

Scan speed 10 m/s

Spot size (diameter) 45350 m

Repetition rate 820 Hz

Energy densitya 0.73.0 J/cm2

Mass spectrometer parametersForward power 1250 W

HV 10 kV

Scan optimization Speed

Number of pre-scans 1

Active dead time 25 ns

Cool gas ow 16 L/min

Auxiliary gas ow 1.5 L/min

Sample gas ow 0.7 L/min

Carrier (He) gas ow 1.1 L/min

Cones Ni-alloy

a Laser parameters were programmed to produce ideal photon uences between 1

and 2 J/cm2.

658 R. Arevalo Jr., W.F. McDonough / Earth and Planetary Science Letters 272 (2008) 656665


4/10


5/10


6/10

represents the W/U ratio of the modern mantle. The average W/U

ratio of our comprehensive sample suite, and thus of the mantle, is

0.650.45 (2; n =86), which is statistically indistinguishable from

the value obtained considering only MORB (W/UMORB =0.650.41,

n=52), OIB (W/UOIB=0.630.07, n =10), or BABB (W/UBABB=0.620.09,

n=12).

The W/U ratio of the modern mantle is also coincident with that of

the continental crust (W/U=0.770.33, 2;Rudnick and Gao, 2003),which is largely based on upper-crustal sediments and loess deposits

(median W/U0.8) and high-grade metamorphic terrains representa-

tive of the lower crust (median W/U 0.8; data fromNewsom et al.,

1996 and references cited therein). Therefore, the W/U ratio of

the mantle may also be inferred to be representative of the entire

silicate portion of the Earth, assuming the absence of a hidden

repository with a W/U ratio outside the range displayed by sampled

reservoirs (McDonough, 1991; Lassiter, 2004; Boyet and Carlson,

2005; Tolstikhin and Hofmann, 2005; Boyet and Carlson, 2006;

Tolstikhin et al., 2006). Assuming a U concentration of 208 (2) ng/g

in the bulk silicate Earth (McDonough and Sun, 1995; Palme and

O'Neill, 2003; Lyubetskaya and Korenaga, 2007) and a W/U ratio of

0.650.45 (2), the concentration of W in the silicate portion of the

Earth is 1310 ng/g.

Fig. 1. Correlations between our LA-ICP-MS concentration data and those of previously published and/or recently acquired solution analyses of the same samples. Previously

published values of Ba, Th and U include isotope dilution measurements fromLoock et al. (1990), solution ICP-MS measurements fromNiu and Batiza (1997), and isotope dilution

analyses of the homogeneous MPI-DING and USGS reference glasses byJochum et al. (2005, 2006). In regards to W, both natural samples (2384-9 and JdF MORB) and geologic

reference glasses (BIR-1g, BHVO-2g, and BCR-2g) were analyzed by laser ablation and solution ICP-MS at the University of Maryland, including via both isotope dilution and high-

precision standard addition methods. Details of these measurements are provided in the Supplementary materials. In all cases, our laser measurements agree well with solution

measurements (within 3%) over several orders of magnitude for each element. Deviations from a perfect correlation with slopem =1.00 can be accounted for by the uncertainty in

each of our measurements, which typically range from 25% (2m).

Fig. 2. W/Ba, W/Th and W/U ratios plotted against the W concentration (ng/g) of our

samples. A perfectly constant element ratio would yield a slope of zero. The

accompanying statistics suggest a systematic decrease in both W/Th and W/U as a

function of increasing W concentration, but this represents an articial bias due to the

higher absolute value of the y-variables of these curves compared to W/Ba.



7/10

Newsom et al. (1996)and Rudnick and Gao (2003)reported that

the bulk continental crust (~0.5% of the bulk silicate Earth, by mass)

contains approximately 1000 300 (2) ng/g W. Based on mass ba-

lance contributions and our preferred estimate of W in the silicate

Earth, the mean concentration of W in the Earth's modern mantle

reservoir is calculated to be 8.37.1 ng/g (with MORB and OIB repre-

senting depleted and enriched source regions, respectively). Based on

the unweighted mean W/Hf ratio of carbonaceous chondrites (W/

Hf= 0.91 0.06, 2m;Kleine et al., 2004b), a silicate Earth compositionwith 280 60 (2) ng/g Hf, and negligibleHf in the core, the bulk Earth

contains 172 36 ng/g W. Accordingly, simple core-modeling and mass

balance considerationspredict that the core has500 120 ng/g W; this

indicates a W metal/silicate partition coefcient (Dmetal/silicate) of ~40

during the conditions of core formation, which is consistent with a

deep (N700 km), potentially hydrous magma ocean early in Earth's

history, according to high pressure-temperature metal/silicate parti-

tioning experiments (Righter et al., 1997; Righter and Drake, 1999;

Righter, 2003).

5.2. Implications for the composition of the DMM and deep mantle

The MORB source, often referred to as the depleted MORB mantle(or DMM), is generally thought to have formed as the result of an

ancient depletion (i.e., continent formation). Although the source of

MORB has been established to be compositionally heterogeneous (e.g.,

van Kekenet al., 2002 and references therein), the relative depletion of

this reservoir, as a whole, remains unsettled; this is largely due to

difculties in modeling the incompatible element budget of the DMM

(Jagoutz et al., 1979; Hofmann, 1988, 2003).

Several studies have attempted to model the composition of the

MORB source by analyzing the trace element chemistry of abyssal

peridotites, calculating parentdaughter ratios of radiogenic isotopes,

and using constant elemental concentration ratios. Assuming a chon-

dritic original composition and a two-stage evolution of the conti-

nental crust, Salters and Stracke (2004) estimated an average DMM

composition with 4.71.4 (2) ng/g U. This model represents a ~4depletion of the highly incompatible elements in the MORB source

relative to the unfractionated silicate Earth, which is more depleted

than the DMM composition of Boyet and Carlson (2006), which as-

sumes a non-chondritic origin, but less depleted than theWorkman

and Hart (2005) model, which follows a gradual evolution of the

continental crust. In order to further investigate the depletion of the

DMM, we may also consider the incompatible trace element che-

mistry of global MORB in conjunction with simple partial melting

dynamics. MORB from typical segments of mid-ocean ridges

(those found far from known plumes or subduction zones) exhibit

a mean composition of 16 13 (2) g/g Ba (Su, 2002), a highly

incompatible element comparable to U. Assuming 812% partial

melting of the MORB source (e.g., Hofmann, 1988), this indicates that

the DMM has approximately 1.61.3 g/g Ba, verifying a factor of ~4

Fig. 3.Loglog co-variation diagram plotting the concentrations (ng/g) of Ba, Th and U

versus the concentration of W in our MORB samples. On this type of plot, because the

plotted samples share the same mantle source region (the depleted MORB mantle, or

DMM), a regression line of slope 1.00 represents a perfectly constant element ratio,

whereas a slope ofN 1.00 indicates a more incompatible lithophile element (e.g., Ba, Th

and U) during mantle melting. It can be seen that the linear regression between W andU yields the slope nearest unity (m =1.040.18, 95% condence) and with the least

statistical scatter (r2 =0.777). Although both Ba and Th yield slopes greater than unity,

suggesting that they are more incompatible than W during mantle melting, the slope of

log Th versus log W is within uncertainty of unity (m =1.10 0.20, 95% condence).

Fig. 4. The W/U ratio of our samples plotted against MgO (wt.%) content. The W/U ratios

of ourmodern basalts appearto beindependent of thedegree of silicate processing, and

no systematic differences among the different sample populations (including N-MORB,

E-MORB, convergent margin volcanics, and intraplate basalts) can be seen with regards

to W/U.

Fig. 5. Models of coremantle exchange as detected by W isotopes (adapted from

Brandon and Walker, 2005). Mixing between a model outer core (with 500 ng/g W,

182W =2.1) and several potential Hawaiian sources. A Hawaiian source equal to the

mean modern mantle (8.3 ng/g W) cannot account for the lack of182Wdepletions in

the Hawaiian picrites suggested by Brandon et al. (1998, 1999) to record a core

signature; this mixing trend mirrors the preferred coremantle mixing curve of

Scherstn et al. (2004). However, a more enriched source equal to two times the silicate

Earth (26 ng/g W), which is consistent with a deep mantle source dened below

~1600 km depth, could account for the W isotopic signaturesof the Hawaiian picrites. A

Hawaiian source comprised of a silicate Earth component (13 ng/g W) plus 5 wt.%

continental crust (CC) could also explain the picrite data. Parameters for the continental

crustal component were taken fromScherstn et al. (2004).



8/10

depletion of highly incompatible elements in the MORB source

compared to the bulk silicate Earth. According to the Salters and

Stracke (2004)depletion model, the DMM is estimated to have 3.0

2.3 (2) ng/g W.

Constraining the mean abundance of W in the modern mantle and

the composition of the MORB source region allows us to make some

inferences as to the composition of the deep mantle, which has been

shown to be geochemically distinct from the DMM (e.g., Hofmann,

1997). If we assume an upper and lower mantle separated by the

660 km discontinuity, this would necessitate ~10 ng/g W in the lower

mantle, according to mass balance and a DMM composition of 3.0

2.3 ng/g W. However, it has been widely demonstrated that the

660 km discontinuity cannot serve as a chemical boundary, as a sig-

nicant mass ux across this depth has been established by tomo-graphic studies (e.g., Creager and Jordan, 1984; Davies and Richards,

1992; Grand et al., 1997; van der Hilst et al., 1997; Montelli et al., 2004;

Nolet et al., 2006). Recently, seismological, geochemical and geophy-

sical observations have identied a potentially deeper boundary

layer between the upper and a heterogeneous deep mantle (e.g.,

Garnero, 2000and references therein). A boundary layer at ~ 1600 km

depth, as preferred by Kellogg et al. (1999), would require an

enriched deep mantle W abundance of ~25 ng/g, or roughly two

times the W content of the unfractionated silicate Earth. Further, if we

consider near-whole-mantle convection with the DMM constituting

the entire mantle mass minus a 200300 km thick boundary layer at

the coremantle boundary (which could serve as the early enriched

reservoir invoked by Tolstikhin and Hofmann, 2005; Boyet and

Carlson, 2005, 2006; Tolstikhin et al., 2006), this reservoir wouldcontain ~190 ng/g W.

As an additional consideration, we can examine the constancy of

the W/Th ratio in our basaltic dataset. Although the W/Th ratio in

the mantle is more variable than W/U because it can be affected to

some degree by partial melting (Fig. 3) and hydrothermaluids (Noll

et al., 1996), the mean W/Th ratio of our oceanic basalts (W/Th=0.19

0.15, 2) is comparable to the MORB and OIB dataset ofNewsom et al.

(1996; W/Th= 0.15 0.11, 2). As such, if the W/Th ratio of the

modern mantle is dened by our basaltic dataset, the mean

mantle has a Th/U ratio of 3.3 1.4 (2), which is higher than

estimates of theMORB source (e.g.,2.5; Turcotte et al., 2001) but lower

than the preferred value for the silicate Earth (e.g., 3.9; McDonough

and Sun, 1995) and chondritic meteorites (e.g., 3.8; Rocholl and

Jochum, 1993).

5.3. Detecting coremantle interactions through W isotopes

Excesses of isotope182W are produced via beta-decay of the now-

extinct 182Hf nuclide, which has a half-life of 8.900.09 Ma ( Vock-

enhuber et al., 2004). Both Hf andW arerefractoryelements, but differ

in their geochemical afnities; under the reducing conditions of core

formation, Hf acts as a lithophile element, and thus prefers to remain

in silicate phases, whereas W behaves as a moderately siderophile

element. Consequently, a metallic core will have a Hf/W ratio of ~0and will therefore retain its original W isotopic composition. Because

of the short-lived nature of this radiogenic system, any existing W

isotopic heterogeneities within the Earth must have been inherited

during the rst ~ 50 Ma of solar system history, the functional lifetime

of182Hf.

Studies of terrestrial samples and chondritic meteorites have

established that thecore of theEarth must be depleted by ~2 parts per

10,000 (or 2 -unit) in 182W relative to the silicate Earth (Kleine et al.,

2002; Schoenberg et al., 2002, Yin et al., 2002). Because the

concentration of W is signicantly greater in the core compared to

the mantle, small depletions in 182W (relative to the silicate Earth) in

plume-derived magmas that originate near the base of the mantle

may result from coremantle interactions. However, initial investiga-

tions into the W isotopic composition of several Hawaiianpicrites that

may record a core component in their source (on the basis of resol-

vable enrichments in 186Os187Os;Brandon et al., 1998, 1999) failed to

resolve these rocks from terrestrial standards (Scherstn et al., 2004).

The W content of the three Hawaiian picrites measured by

Scherstn et al. (2004)range from 113 ng/g (H-11) to 313 ng/g (Lo-

02-04), as determined by this study. Assuming 515% partial melting,

this indicates a Hawaiian source with anywhere from 5 to 45 ng/g W.

Assuming a Hawaiian source with a concentration of 26 ng/g W, or

approximately two times the W content of the undifferentiated

silicate Earth (13 ng/g W), the three Hawaiian picrites may be

accounted for by a two end-member mixing scenario between the

outer core and an enriched deep mantle reservoir (Fig. 5). Such an

Fig. 6. Two end-member mixing betweenthe outercore and modelmantle sources. The

light gray eld represents the 2scatter seen in our mantle-derived samples; the dark

gray region represents the 2m. The overall range of W/U seen in modern oceanic

basalts makes assessing coremantle exchange difcult for enriched sources and low

degrees of core contribution. As seen in thegure, even up to 1 wt.% of core material

added toa mantlesource with 8.3ng/gW wouldnot resultin an enriched W/Uoutside

of the spread seen in basaltic sources. However, a more depleted source, such as a

sourceequal tothe Depleted MORB Mantle (i.e.,DMM),wouldallowfor thedetection of

b1.0 wt.% core contribution. Data for the Hawaiian picrites examined by Brandon et al.

(1998,1999)andScherstn et al. (2004)lay above the mean and 2mspread, but easily

reside within the scatter seen in our basaltic samples. This does not preclude a core

component added tothe source of these samples, though, as the source of these picrites

likely hasN

3.0 ng/g W.

Table 3

Siderophile/lithophile element pairs

Element Silicate earth (g/g)a Core (g/g)b Core/SE enrichment factor

P 90 2000 22

Ti 1200 0 0.0

Mn 1045 300 0.3

Fe 62,600 855,000 14

Mo 0.05 5 100

Pd 0.004 3.1 775

Ba 6.6 0 0.0Ce 1.68 0 0.0

Nd 1.25 0 0.0

Yb 0.44 0 0.0

W 0.0131 0.504 38

Re 0.0003 0.23 767

Pb 0.15 0.4 2.7

Fe/Mn 60 2850 N10

P/Nd 72 N105 N103

Pb/Ce 0.089 N103 N104

Mo/Ce 0.030 N104 N105

W/Ba 0.0020 N103 N105

Re/Yb 0.00068 N103 N106

Pd/Ti 3.3E06 N104 N109

a FromMcDonough and Sun (1995), excepting W.b FromMcDonough (2003), excepting W.



9/10

enriched Hawaiian source is consistent with a lower mantle source

dened below ~1600 km depth, as originally suggested by Kellogg

et al. (1999), and may result from pyroxenitic melting in the Hawaiian

source region (Sobolev et al., 2005, 2007). Additionally, as Brandon

and Walker (2005)observed, even modest contamination by a crustal

component could overprint any W core signature recorded in these

rocks while having a negligible effect on their Os isotopic ratios. This is

illustrated in the model source consisting of a silicate Earth com-

ponent, with 13 ng/g W, mixed with 5 wt.% continental crust inFig. 5.Although higher-precision measurements of the W isotopic composi-

tions of these rocks might provide some clarity to these issues, an

additional window into detecting coremantle exchange may lie with

the terrestrial W/U ratio.

5.4. Detecting coremantle interactions through W concentration ratios

Whereas isotopic ratios can serve as geochemical tracers of either

the physical admixture of or diffusive isotopic exchange between the

core and mantle (Puchtel and Humayun, 2000), concentration ratios

can only act as a proxy of the physical admixture of these two

reservoirs, assuming the core and silicate Earth (including both the

modern mantle and continental crustal reservoirs) each have a unique

and constant value. Because core formation has depleted the silicate

Earth in siderophile elements relative to the lithophile elements,

siderophile-to-lithophile ratios provide the most sensitive type of

tracers because such ratios are extremely high in the core and cor-

respondingly low in the silicate Earth (Table 3). For example, Fe/Mn

ratios, which have been implicated in the identication of a core

signature in modern Hawaiian lavas (Humayun et al., 2004), are

enriched in the core relative to the mantle, but only by a factor ofN10.

On the other hand, the W/U of the core is enriched by a factor N105

relative to the modern mantle. As a result, W/U is potentially three-

times more sensitive than Fe/Mn to a two end-member mixing

scenario between the mantle and 1 wt.% of core material, considering

the reservoir compositions listed inTable 3.

Since the core contains approximately 95% of the bulk Earth's W

budget and essentially no U (McDonough, 2003), it can be condently

established that the core has a W/U1000. A two end-membermixing curve between a mantle reservoir with 8.3 ng/g W and W/

U=0.650.45 (2) and an outer core reservoir with ~500 ng/g W and

W/U=1000 (as a lower limit), however, indicates that the physical

entrainment of up to 1 wt.% of outer core materials would fail to result

in a resolvable increase in W/U; a more depleted source composition

(e.g., DMM with 3.0 ng/g W) or a higher degree of core contamination

is required for coremantle exchange to be identied through the use

of this proxy (Fig. 6). An analysis of the three Hawaiian picrites

examined byBrandon et al. (1998, 1999)and Scherstn et al. (2004)

illustrates these limitations. Although all three of the picrites reside

withinthe variabilityseen in oursample suite, this does not preclude a

core component added to the source of these rocks. Brandon et al.

(1998,1999)suggest that these three picrites carry only 0.30.5% core

contribution; this amount of mass exchange is permitted with ourmixing models assuming a Hawaiian source with an enriched mantle

composition. Thus, although W/U serves as a potentially sensitive

geochemical tracer of physical admixture between outer core and

deep mantle materials, the variability seen in modern basaltic samples

makes it difcult to unambiguously detect core contributions in

materials derived from enriched source regions.

6. Conclusions

Modern oceanic basalts, including both E-type and N-type MORB,

intraplate and convergent margin volcanics, reveal that U behaves

analogously to W during silicatedifferentiation. The averageW/U ratio

of these samples (0.650.45, 2,n =86) is representative of both the

modern mantle and bulk silicate Earth, and suggests a bulk silicate

Earth composition of 1310 ng/g W and a mean modern mantle

composition of 8.3 7.1 ng/g W. According to the model DMM

composition of Salters and Stracke (2004), the MORB source likely

contains 3.02.3 ng/g W. Assuming a stratied mantle at ~1600 km

depth, this indicates a deep mantle with ~25 ng/g W. Alternatively,

considering near-wholemantleconvectionwithonly a ~250 km thick

Dlayer at the coremantle boundary, this reservoir must be enriched

up to ~190 ng/g W.

In theory, both W isotopes and W/U ratios can be used to identifycoremantle exchange. However, as with most geochemical tracers of

internal processes within the Earth, these proxies are dependent

on the source composition of the sampled materials. Three Hawaiian

picrites initially examined byBrandon et al. (1998, 1999)have been

suggested to record a core signature according to their 186Os187Os

isotopic compositions. However, no discernable core signature is seen

via W isotopes or W/U ratios. This suggests either (1) the lack of a core

component in the source of these rocks, (2) crustal contamination of

thesamples, or (3)a source with at least 26 ng/g W, which is consistent

with a deep mantlesource dened below ~1600 km. Accordingly, until

further constraints can be placed on the source region of these

samples, the issue of coremantle exchange has yet to be resolved.

Acknowledgements

We would like to thank the Division of Petrology and Volcanology,

Department of Mineral Sciences, Smithsonian Institute, especially

Leslie Hale, Sorena Sorenson and the late Jim Luhr, for providing us

with so many precious samples to conduct this study. We also appre-

ciate the sample donations generously afforded by Michael Garcia,

Thomas Ireland, Emily Klein, Charles Langmuir, Gaby Loock, Yaoling

Niu, Marc Norman, and Michael Pert. This study could not have been

conducted without the analytical prowess of Richard Ash, who helped

us develop the analytical protocol for our LA-ICP-MS method, or the

helpful reviews of Rick Carlson, James Day, John Lassiter, Adam

Mansur, Carsten Mnker, Sune Nielsen, and Richard Walker. Special

thanks go to Thorsten Kleine and Tetsuya Yokoyama for their

assistance with developing our W isotope dilution procedures. This

study was funded by NSF grant # 0337621 and #0739006.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, in

the online version, atdoi:10.1016/j.epsl.2008.05.031.

References

Bevington, P.R., Robinson, D.K., 2003. Data Reduction and Error Analysis for the PhysicalSciences. McGraw-Hill, New York, NY.

Boyet, M., Carlson, R.W., 2005. 142Nd evidence for early(N4.53 Ga) global differentiationof the silicate Earth. Science 309, 576581.

Boyet,M., Carlson, R.W., 2006. A newgeochemicalmodelfor theEarth's mantleinferredfrom 146Sm142Nd systematics. Earth Planet. Sci. Lett. 250, 254268.

Brandon, A.D., Walker,R.J.,2005.The debateovercoremantle interaction. EarthPlanet.Sci. Lett. 232, 211225.

Brandon, A.D., Walker, R.J., Morgan, J.W., Norman, M.D., Prichard, H.M., 1998. Coupled186Os and 187Os evidence for coremantle interaction. Science 280, 15701573.

Brandon, A.D., Norman, M.D.,Walker, R.J.,Morgan, J.W.,1999.186Os187Os systematics ofHawaiian picrites. Earth Planet. Sci. Lett. 174, 2542.

Creager, K.C., Jordan, T.H.,1984. Slab penetration into the lower mantle. J. Geophys. Res.89, 30313049.

Crisp, J.A., 1984. Rates of magma emplacement and volcanic output. J. Volc. Geotherm.Res. 20, 177211.

Davies, G.F., Richards, M.A., 1992. Mantle convection. J. Geol. 100, 151206.Eggins, S.M., Shelley, J.M.G., 2002. Compositional heterogeneity in NIST SRM 610-617

glasses. Geostd. News. 26, 269286.Eggins, S.M., Rudnick, R.L., McDonough, W.F., 1998. The composition of peridotites and

their minerals: a laser-ablation ICP-MS study. Earth Planet. Sci. Lett. 154, 5371.Garnero, E.J., 2000. Heterogeneity of thelowermost mantle. Annu. Rev.EarthPlanet. Sci.

28, 509537.Grand, S., van der Hilst, R.D., Widiyantoro, S., 1997. Global seismic tomography:

a snapshot of convection in the Earth. GSA Today 7, 1

7.

http://dx.doi.org/doi:10.1016/j.epsl.2008.05.031http://dx.doi.org/doi:10.1016/j.epsl.2008.05.031http://dx.doi.org/doi:10.1016/j.epsl.2008.05.031


10/10

Hofmann, A.W.,1988. Chemical differentiation of the Earth the relationship betweenmantle, continental-crust, and oceanic-crust. Earth Planet. Sci. Lett. 90, 297314.

Hofmann, A.W., 1997. Mantle geochemistry: the message from oceanic volcanism.Nature 385, 219229.

Hofmann,A.W., 2003.Samplingmantleheterogeneitythrough oceanic basalts:isotopesandtraceelements,The Mantleand Core (ed. R.W. Carlson) Vol.2 Treatiseon Geochemistry(eds. H.D. Holland and K.K Turekian). Elsevier-Pergamon, Oxford, pp. 61101.

Hofmann, A.W., Jochum, K.P., Seufert, M., White, W.M., 1986. Nb and Pb in oceanicbasalts new constraints on mantle evolution. Earth Planet. Sci. Lett. 79, 3345.

Humayun, M., Qin, L.P., Norman, M.D., 2004. Geochemical evidence for excess iron inthe mantle beneath Hawaii. Science 306, 9194.

Jacobsen, S.B., 2005. The Hf-W isotopic system and the origin of the earth and moon.Annu. Rev. Earth Planet. Sci. 33, 531570.Jagoutz, E., Palme, H., Baddenhausen, H., Blum, K., Cendales, M., Dreibus, G., Spettel, B.,

Lorenz, V., Wanke, H., 1979. The abundances of major, minor and trace elements inthe earth's mantle as derived from primitive ultramac nodules. 10th Proceedingsof Lunar and Planetary Sciences, pp. 20312050.

Jochum, K.P., McDonough, W.F., Palme, H., Spettel, B., 1989. Compositional constraintson the continental lithospheric mantle from trace elements in spinel peridotitexenoliths. Nature 340, 548550.

Jochum, K.P., Stoll, B., Herwig, K ., Willbold, M., Hofmann, A.W., Amini, M., Aarburg, S.,Abouchami, W., Hellebrand, E., Mocek, B., Raczek, I., Stracke, A., Alard, O., Bouman,C., Becker, S., Ducking, M., Bratz, H., Klemd, R., de Bruin, D., Canil, D., Cornell, D., deHoog, C.J., Dalpe, C., Danyushevsky, L., Eisenhauer, A., Premo, W.R., Sun, W.D.D.,Tiepolo, M., Vannucci, R., Vennemann, T., Wayne, D., Woodhead, J.D., 2006. MPI-DING reference glasses for in situ microanalysis: new reference values for elementconcentrations and isotope ratios. Geochem. Geophys. Geosyst. 7, 144.

Jochum, K.P., Willbold, M., Raczek, I., Stoll, B., Herwig, K., 20 05. Chemical characterisa-tion of the USGS reference glasses GSA-1G, GSC-1G, GSD-1G, GSE-1G, BCR-2G,BHVO-2G and BIR-1G using EPMA, ID-TIMS, ID-ICP-MS and LA-ICP-MS. Geostd.

Geoanal. Res. 29, 285302.Jochum, K.P., Stoll, B., Herwig, K., Willbold, M., 2007. Validation of LA-ICP-MS trace

element analysis of geological glasses using a new solid-state 193 nm Nd:YAG laserand matrix-matched calibration. J. Anal. Atom. Spec. 22, 112121.

Kellogg, L.H., Hager, B.H., van der Hilst, R.D., 1999. Compositional stratication in thedeep mantle. Science 283, 18811884.

Kleine, T., Munker, C., Mezger, K., Palme, H., 2002. Rapid accretion and early coreformation on asteroids and the terrestrial planets from HfW chronometry. Nature418, 952955.

Kleine, T., Mezger, K., Palme, H., Munker, C., 2004a. The W isotope evolution of the bulksilicate Earth: constraints on the timing and mechanisms of core formation andaccretion. Earth Planet. Sci. Lett. 228, 109123.

Kleine, T., Mezger, K., Munker, C., Palme, H., Bischoff, A., 2004b. 182Hf182W isotopesystematics of chondrites, eucrites, and martian meteorites: chronology of coreformation and early mantle differentiation in Vesta and Mars. Geochim.Cosmochim. Acta 68, 29352946.

Kleine, T.,Mezger,K., Palme, H.,Scherer,E., Munker,C.,2005a.Earlycore formation in asteroidsand late accretion of chondrite parent bodies: evidence from182Hf182W in CAIs, metal-rich chondrites, and iron meteorites. Geochim. Cosmochim. Acta 69, 58055818.

Kleine, T., Palme, H., Mezger, M., Halliday, A.N., 2005b. HfW chronometry of lunarmetals and the age and early differentiation of the Moon. Science 310,16711674.

Lassiter, J.C., 2004. Role of recycled oceanic crust in the potassium and argon budget ofthe Earth: toward a resolution of the missing argonproblem. Geochem. Geophys.Geosyst. 5, 116.

Loock, G., McDonough, W.F., Goldstein, S.L., Hofmann, A.W., 1990. Isotopic compositionsof volcanic glasses from the Lau Basin. Marine Mining 9, 235245.

Lyubetskaya, T., Korenaga, J., 2007. Chemical composition of Earth's primitive mantleand its variance: 1. Method and results. J. Geophys. Res. 112, B03212. doi:10.1029/2005JB004224.

McDonough, W.F., 1991. Partial melting of subducted oceanic crust and isolation of itsresidual eclogitic lithology. Phil. Trans. Roy. Soc. Lond. 335, 407418.

McDonough, W.F., 2003. Compositional model for the Earth'score, The Mantle and Core(ed. R.W. Carlson) Vol. 2 Treatise on Geochemistry (eds. H.D. Holland and K.KTurekian). Elsevier-Pergamon, Oxford, pp. 547568.

McDonough, W.F., Sun, S.S., 1995. The composition of the Earth. Chem. Geol. 120,223253.

Montelli, R., Nolet, G., Dahlen, F.A., Masters, G., Engdahl, E.R., Hung, S.H., 2004. Finite-

frequencytomographyreveals avariety ofplumesin themantle.Science 303,338

343.Newsom, H.E., 1990. Accretion and core formation in the Earth: evidence from

siderophile elements. In: Newsom, H.E., Jones, J.H. (Eds.), Origin of Earth. OxfordPress, pp. 273288.

Newsom,H.E., Palme, H.,1984. The depletion of siderophile elementsin the Earth's mantlenew evidence from molybdenum and tungsten. Earth Planet. Sci. Lett. 69, 354364.

Newsom, H.E., White, W.M., Jochum, K.P., Hofmann, A.W., 1986. Siderophile andchalcophile element abundances in oceanic basalts, Pb-isotope evolution andgrowth of the Earth's core. Earth Planet. Sci. Lett. 80, 299 313.

Newsom, H.E., Sims, K.W.W., Noll, P.D., Jaeger, W.L., Maehr, S.A., Beserra, T.B., 1996. Thedepletion of tungsten in the bulk silicate Earth: constraints on core formation.Geochim. Cosmochim. Acta 60, 11551169.

Niu, Y.L., Batiza, R., 1997. Trace element evidence from seamounts for recycled oceaniccrust in the eastern Pacic mantle. Earth Planet. Sci. Lett. 148, 471483.

Nolet, G., Karato, S.I., Montelli, R., 2006. Plume uxes from seismic tomography. EarthPlanet. Sci. Lett. 248, 685699.

Noll, P.D., Newsom, H.E., Leeman, W.P., Ryan, J.G., 1996. The role of hydrothermaluidsin the production of subduction zone magmas: evidence from siderophile andchalcophile trace elements and boron. Geochim. Cosmochim. Acta 60, 587611.

Norman, M.D., Grifn, W.L., Pearson, N.J., Garcia, M.O., O'Reilly, S.Y., 1998. Quantitativeanalysis of traceelement abundancesin glassesand minerals: a comparison of laserablation inductively coupled plasma mass spectrometry, solution inductivelycoupled plasma mass spectrometry, proton microprobe and electron microprobedata. J. Analyt. Atom. Spec. 13, 477482.

Palme, H., Rammensee, W., 1981. The signicance of W in planetary differentiationprocesses: evidence from new data on eucrites. 12th Lunar and Planetary SciencesConference, pp. 949964.

Palme, H. and O'Neill, H.S.C., 2003. Cosmochemical estimates of mantle composition,The Mantle and Core (ed. R.W. Carlson) Vol. 2 Treatise on Geochemistry (eds. H.D.Hollandand K.K Turekian). Elsevier-Pergamon, Oxford, pp. 138.

Pearce, N.J.G., Perkins, W.T., Westgate,J.A., Gorton, M.P., Jackson, S.E.,Neal, C.R.,Chenery,S.P.,1997. A compilation of newand published major andtrace element datafor NISTSRM 610 and NIST SRM 612 glass reference materials. Geostd. News. 21,115144.

Puchtel, I., Humayun, M., 2000. Platinum group elements in Kostomuksha komatiitesand basalts: Implications for oceanic crust recycling and coremantle interaction.Geochim. Cosmochim. Acta 64, 42274242.

Righter,K., 2003.Metalsilicate partitioning of siderophileelements and coreformationin the early Earth. Annu. Rev. Earth Planet. Sci. 31, 135174.

Righter, K.,Drake, M.J.,1999. Effectof wateron metalsilicate partitioning of siderophileelements: a high pressure and temperature terrestrial magma ocean and coreformation. Earth Planet. Sci. Lett. 171, 383399.

Righter, K., Shearer, C.K., 2003. Magmatic fractionation of Hf and W: constraints on thetiming of core formation and differentiation in the Moon and Mars. Geochim.Cosmochim. Acta 67, 24972507.

Righter, K., Drake, M.J., Yaxley, G., 1997. Prediction of siderophile element metalsilicatepartition coefcients to 20 GPa and 2800 degrees C: the effects of pressure,temperature, oxygen fugacity, and silicate and metallic melt compositions. Phys.Earth Planet. Int. 100, 115134.

Rocholl, A., Jochum, K.P., 1993. Th, U and other trace-elements in carbonaceous

chondrites implications for the terrestrial and solar-system Th/U ratios. EarthPlanet. Sci. Lett. 117, 265278.

Rudnick, R.L. and Gao, S., 2003. Composition of the continental crust, The Crust (ed. R.L.Rudnick) Vol. 3 Treatise on Geochemistry (eds. H.D. Holland and K.K Turekian).Elsevier-Pergamon, Oxford, pp. 164.

Salters, V.J.M., Stracke, A., 2004. Composition of the depleted mantle. Geochem.Geophys. Geosyst. 5, 127.

Scherstn, A., Elliott, T.,Hawkesworth,C., Norman, M.,2004. Tungsten isotope evidence thatmantle plumes contain no contribution from the Earth's core. Nature 427, 234237.

Schoenberg, R., Kamber, B.S., Collerson, K.D., Eugster, O., 2002. New W-isotope evidencefor rapid terrestrial accretion and very early core formation. Geochim. Cosmochim.Acta 66, 31513160.

Sims, K.W., Newsom, H.E., Gladney, E.S., 1990. Chemical fractionation during formationof the Earth's core andcontinental crust:clues fromAs, Sb,W, andMo. In:Newsom,H.E., Jones, J.H. (Eds.), Origin of Earth. Oxford Press, pp. 291 317.

Sims, K.W.W., DePaolo, D.J., 1997. Inferences about mantle magma sources fromincompatible element concentration ratios in oceanic basalts. Geochim. Cosmo-chim. Acta 61, 765784.

Sobolev, A.V., Hofmann, A.W., Kuzmin, D.V., Yaxley, G.M., Arndt, N.T., Chung, S.L.,Danyushevsky, L.V., Elliott, T., Frey, F.A., Garcia, M.O., Gurenko, A.A., Kamenetsky, V.S.,Kerr, A.C.,Krivolutskaya,N.A., Matvienkov,V.V., Nikogosian, I.K.,Rocholl, A., Sigurdsson,I.A., Sushchevskaya, N.M., Teklay, M., 2007. The amount of recycledcrust in sources ofmantle-derived melts. Science 316, 412417.

Sobolev, A.V., Hofmann, A.W., Sobolev, S.V., Nikogosian, I.K., 2005. An olivine-freemantle source of Hawaiian shield basalts. Nature 434, 590597.

Su, Y.J., 2002. Mid-ocean ridge basalt trace element systematics: constraints fromdatabase management, ICP-MS analyses, global data compilation, and petrologicmodeling, Ph.D. Columbia University, pp. 457.

Sun, S.S., 1982. Chemical composition and origin of the earth's primitive mantle.Geochim. Cosmochim. Acta 46, 179192.

Sun, S.-s., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts:implications for mantle composition and processes. Magmatism in the OceanBasins, vol. 42. Geological Society Special Publication.

Taylor, S.R., McLennan, S.M., 1985. The Continental Crust: Its Composition andEvolution. Blackwell, Oxford.

Tolstikhin, I., Hofmann, A.W., 2005. Early crust on top of the Earth's core. Phys. EarthPlanet. Int. 148, 109130.

Tolstikhin, I.N., Kramers, J.D., Hofmann, A.W., 2006. A chemical Earth model with wholemantle convection: the importance of a coremantle boundary layer (D) and itsearly formation. Chem. Geol. 226, 7999.

Turcotte, D.L., Paul, D., White, W.M., 2001. Thoriumuranium systematics requirelayered mantle convection. J. Geophys. Res. 106, 42654276.

van der Hilst, R.D., Widiyantoro, S., Engdahl, E.R., 1997. Evidence for deep mantlecirculation from global tomography. Nature 386, 578584.

van Keken, P.E., Hauri, E.H., Ballentine, C.J., 2002. Mantle mixing: the generation,preservation, and destruction of chemical heterogeneity. Annu. Rev. Earth Planet.Sci. 30, 493525.

Vockenhuber,C., Oberli,F., Bichler, M.,Ahmad,I., Quitte,G., Meier,M., Halliday, A.N., Lee,D.C.,Kutschera, W.,Steier, P., Gehrke,R.J.,Helmer, R.G., 2004.Newhalf-lifemeasurementof182Hf: improved chronometer for the early solar system. Phys. Rev. Lett. 93, 14.

Workman, R.K., Hart, S.R., 2005. Major and trace element composition of the depletedMORB mantle (DMM). Earth Planet. Sci. Lett. 231, 5372.

Yin, Q.Z., Jacobsen, S.B., Yamashita, K., Blichert-Toft, J., Telouk, P., Albarde, F., 2002.A short timescale for terrestrial planet formation from HfW chronometry ofmeteorites. Nature 418, 949952.

http://dx.doi.org/10.1029/2005JB004224http://dx.doi.org/10.1029/2005JB004224http://dx.doi.org/10.1029/2005JB004224http://dx.doi.org/10.1029/2005JB004224http://dx.doi.org/10.1029/2005JB004224

Date post:	03-Jun-2018
Category:	Documents
Upload:	paul-quispe-solano
View:	221 times
Download:	0 times

Arevalo Tungsten Geochem 2008

Documents